The present invention relates to a brake disc for a disc brake of a motor vehicle.
The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention.
Conventionally a brake-disc friction ring is produced in the casting process—usually sand casting—from high carbon grey cast iron. For various reasons grey cast iron is an optimal material for friction bodies. In multiple applications the carrier part of the brake disc has long been produced from aluminum or aluminum alloys in order to save weight. In these constructions it is considered important that the friction ring and the brake-disc chamber are radially movable relative to each other in order to minimize thermal tensions, which occur in the friction ring during each braking procedure. The radial degree of freedom is generated via a fit clearance, which is generated by mechanical processing and an inserted connecting element. For conceptual reasons the complex mechanical processing between the casting processes and the required fit tolerances causes high manufacturing costs. Such a brake disc is for example disclosed in EP 2 275 702 B1. A generic brake disc, which has internal ventilation and includes a pot-shaped carrier part, a friction ring, and multiple connecting elements distributed in circumferential direction of the disc brake and extending in radial direction, and configured as separate components, wherein the carrier part and the friction ring are fixedly interconnected in radial direction via the multiple connecting elements, wherein the connecting elements are form fittingly connected with the carrier part is known from DE 101 03 639 A1.
According to the teaching of DE 101 0-3 639 A1 the connection between the carrier part and the connecting elements is configured as form fitting connection, while the fastening between the friction ring and connecting elements is realized by material union, for example by welding or soldering. Due to the material connection between the friction ring and the connecting elements only an unsatisfactory (unfavorable) fastening is achieved with regard to quality and position of the connection. While soldering connections become lose at temperatures above the melting temperature of the soldering medium and as a result represent an undefined connection, welding connections tend to have reduced strength in the edge regions due to changes in microstructure.
A material connection which partially or entirely loosens under the influence of high temperature can lead to a reversible and/or irreversible deformation (axial run-out, waviness, unbalance) of the brake disc. This promotes undesired uneven wear on the friction ring and thus leads to so-called “brake judder” which adversely affects driving comfort. As the case may be, a lasting deformation of the brake disc can lead to non-functioning of the entire braking system.
Because in addition, material connections are characterized by a high heat conductivity, they facilitate a high heat transfer from the friction ring to the connecting elements. This in turn results in the fact that an increased heat introduction into the carrier part also occurs via the contact sites of the connecting elements to the carrier part.
The temperature differences between the contact sites and the remaining carrier part resulting from this circumstance can also lead to deformation of the carrier part because the outer region of the carrier part expands more than the inner part. Therefore, undesired heat deformation can result, which deforms the carrier part in the manner of a “waviness” and leads to an axial run-out which is transferred to the friction ring.
It would therefore be desirable and advantageous to provide an improved brake disc that has a long service life and also ensures a high driving comfort and a high safety.